Mexico drops plans to distribute maps to guide immigrants safely across the U.S.-Mexico border... another tunnel on that border is discovered… and Colombian authorities say they have dismantled a false passport ring with links to al-Qaida and the Islamic militant group Hamas. Amy Katz takes a look at these stories -- which illustrate the challenges the U.S. faces in securing its borders.

U.S. and Mexican authorities have discovered what officials call the longest and most sophisticated tunnel yet -- running from the Mexican town of Tijuana to just across the border in the U.S. state of California. U.S. officials say it is about one kilometer long.

Mike Unzueta of U.S. Immigration Customs Enforcement announced, "As part of this we have seized approximately 200 pounds (91 kilograms) of marijuana that were on the U.S. side of the tunnel. Reports from Mexico are that the Mexican authorities have seized approximately 4,000 pounds (1800 kilograms) of marijuana."

The U.S. Drug Enforcement Agency says the tunnel was a major gateway for illegal immigrants and drugs coming from Mexico into the U.S. At least 20 tunnels have been found along the U.S. border with Mexico since the September 11th, 2001 terrorist attacks. Four have been found in California this month alone.

In another development, Mexico has suspended a plan to distribute maps intended to guide migrants safely across the U.S.-Mexico border. The map shows migrants the safest routes, including water stations manned by a U.S. humanitarian group. U.S. officials objected to the maps, which they said would encourage more people to cross the border illegally. Mexico says they were meant to warn people of the risks they might face in desert areas along the border where hundreds of migrants died last year.

Meanwhile, officials in Colombia say they have broken up a false passport ring with links to al-Qaida and the Islamic militant group Hamas. Colombian authorities say they have arrested 19 people in connection with the case, whom they say sent the forged Colombian passports to citizens of Pakistan, Jordan, Iraq and Egypt. The passports were then reportedly enabling foreign nationals, possibly terrorists, to travel as though they were Colombians, to the U.S. and Europe.